Optimization of roadway layouts under asymmetric mining height scenarios: A case study of lower-seam extraction in Jining coal mine

This study investigates the complex geomechanical challenges arising from lower-seam roadway layouts when subjected to overlying goafs with asymmetric mining heights. A case study is conducted at the 2113 working face in the Jining Coal Mine, focusing on conditions marked by a large mining height, adjacent goafs of varying heights, high in-situ stress, and severe surrounding rock damage. A coal pillar bearing pressure model and a floor failure mechanical model were developed and optimized to account for the asymmetric loading induced by unequal mining heights on both sides of the coal pillar. Using these models, the stress distribution within the pillar and the failure depth of the floor strata were quantitatively analyzed. Three roadway layout schemes (offset-outside, overlapping, and offset-inside) were proposed and evaluated through numerical simulation and theoretical analysis. The study further integrates the Analytic Hierarchy Process (AHP) with fuzzy comprehensive evaluation to systematically assess and rank the schemes based on safety, economy, and geological adaptability. Results indicate that the offset-inside layout, where the roadway is positioned beneath the goaf outside the pillar stress influence zone, yields the most balanced performance in terms of surrounding rock stability and operational safety. The proposed methodology and findings provide a practical theoretical basis and technical guidance for optimizing roadway layouts under similar asymmetric mining conditions in multi-seam coal mines.